Separation apparatus

ABSTRACT

A configuration of two cyclones for separation of solids from a solids-gas mixture wherein the gas outlet of a first cyclone is fluidly connected to an outlet conduit provided with a gas outlet opening and the gas inlet of the second cyclone is connected to an inlet conduit provided with a gas inlet opening, wherein the outlet conduit and inlet conduit are arranged co-axial such that gas leaving the outlet opening of the outlet conduit enters the inlet opening of the inlet conduit and gas from the exterior of the cyclone configuration can enter the gas inlet opening of the inlet conduit wherein the gas outlet opening and the gas inlet opening are axially spaced away from each other and wherein the interior of the gas outlet tube is provided with means to decrease the swirling motion of the gas passing said outlet conduit.

FIELD OF THE INVENTION

The invention is directed to an improved separation apparatus, whereinparticles can be efficiently separated from a gas-particles mixture. Theinvention is also directed to the use of such an apparatus in a fluidcatalytic cracking process.

BACKGROUND OF THE INVENTION

The field of fluid catalytic cracking (FCC) has undergone significantdevelopment improvements due primarily to advances in catalysttechnology and product distribution obtained therefrom. With the adventof high activity catalysts and particularly crystalline zeolite crackingcatalysts, new areas of operating technology have been encounteredrequiring even further refinements in processing techniques to takeadvantage of the high catalyst activity, selectivity and operatingsensitivity. Of particular concern in this field has been thedevelopment of methods and systems for separating the hydrocarbonproduct from the catalyst particles, particularly from a high activitycrystalline zeolite cracking catalysts, under more efficient separatingconditions so as to reduce the overcracking of conversion products andpromote the recovery of desired products of an FCC operation. Patentpublications EP-A-162978, EP-A-629679, U.S. Pat. No. 5,248,411 andEP-A-604026 all describe developments concerned with the rapidseparation and recovery of entrained catalyst particles from thehydrocarbon products. The rapid separation is achieved in that thecatalyst are separated from the reactor riser effluent in a firstcyclone separator, the primary cyclone, of which gas outlet conduit isin fluid connection with a secondary cyclone. This cyclone line up inFCC reactors is also referred to as close-coupled cyclone separationprovided that the primary and secondary cyclones are contained in onelarger vessel.

This coupling of primary and secondary cyclones minimises the residencetime in which the hydrocarbon product is in contact with the catalystafter it leaves the reactor riser, which limits undesirableaftercracking.

In the connecting conduit between primary and secondary cyclone anopening or slit may be present through which gas may enter from theexterior of the cyclone configuration. Such a slit as disclosed in theabove referred to patent publications is used to allow stripping gas tobe discharged from the FCC reactor together with the hydrocarbonproducts.

Various designs have been proposed for the slit in the connectingconduit. A commonly used design is described in EP-A-162978. In thisdesign the gas inlet opening of the inlet conduit connected to the gasinlet of the secondary cyclone has a larger diameter than the gas outletopening of the outlet conduit connected to the gas outlet of the primarycyclone. In said design the inlet conduit overlaps the outlet conduit.The annular space between the two conduits forms the slit opening. Thetwo conduit parts can move relative to each other. This allows theprimary cyclone, which is usually fixed to the reactor riser, and thesecondary cyclones, which are normally fixed to the roof of the FCCreactor vessel, to move relative to each other during start-up and shutdown operations. Such relative movement will occur due to the differentthermal expansion of the cited different parts in said FCC reactorvessel.

EP-A-613935 describes a configuration of two cyclones for separation ofsolids from a solids-gas mixture wherein the gas outlet of the firstcyclone is fluidly connected to an outlet conduit provided with a gasoutlet opening and the gas inlet of the second cyclone is connected toan inlet conduit provided with a gas inlet opening, wherein the outletconduit and inlet conduit are arranged co-axial such that gas leavingthe outlet opening of the outlet conduit and gas from the exterior ofthe cyclone configuration can enter the gas inlet opening of the inletconduit

A disadvantage of such a slit opening is that coke may grow in theannular space thereby causing the two parts of the conduit to becomefixed relative to each other. During start-up and shut down operationsunacceptable mechanical stress may then be exercised upon the cycloneconfiguration, which may eventually cause serious damage. The object ofthe present invention is to provide a more robust slit design for theclosed-coupled cyclone configuration.

SUMMARY OF THE INVENTION

Configuration of two cyclones for separation of solids from a solids-gasmixture wherein the gas outlet of a first cyclone is fluidly connectedto an outlet conduit provided with a gas outlet opening and the gasinlet of the second cyclone is connected to an inlet conduit providedwith a gas inlet opening. The outlet and inlet conduit are arrangedco-axial such that gas leaving the outlet opening of the outlet conduitenters the inlet opening of the inlet conduit. Gas from the exterior ofthe cyclone configuration can enter the gas inlet opening of the inletconduit. The gas outlet opening and the gas inlet opening are axiallyspaced away from each other. The interior of the gas outlet tube isprovided with means to decrease the swirling motion of the gas passingsaid outlet conduit.

Applicants found that when the outlet conduit of the primary cyclone andthe inlet conduit of the secondary cyclone do not overlap a slit isformed which is less prone to coke formation. Applicants have furtherfound it to be essential that the outlet conduit of the primary cycloneis provided with means to decrease the swirling motion in said conduit.This is advantageous because otherwise the gas would move radialy awayfrom the centre of the conduit and away from to the inlet opening (8) ofthe inlet conduit (7).

The invention is also directed to a FCC reactor comprising the cycloneconfiguration described above, the downstream end of a FCC reactor riserfluidly connected to the inlet opening of the primary cyclone, and a gasoutlet fluidly connected to the gas outlet of the secondary cyclone anda solids outlet at the lower end of the vessel.

The invention is also directed to a catalytic cracking process makinguse of said FCC reactor.

The invention shall be described in more detail below, including somepreferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional presentation of part of aclose-coupled cyclone apparatus in an FCC reactor.

FIG. 2 illustrates the top of the primary cyclone and the up stream endof connecting conduit (7).

FIG. 3 illustrates a top view of the primary cyclone of FIG. 2.

FIG. 4 shows a preferred embodiment of the primary cyclone and theupstream end of connecting conduit (7).

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 represent a preferred embodiment of the apparatus according tothe invention. In the Figure a reactor riser (10) of a fluidizedcatalytic cracking process is shown which is fluidly connected viaconduit (11) to a primary cyclone (1). In the Figure only one primarycyclone separator is shown for clarity reasons. Typically more than one,suitably two or three, primary cyclone separators (1) will be in fluidcommunication with the downstream end (12) of a reactor riser (10). Theprimary cyclone (1) has a tubular housing provided with a tangentiallyarranged inlet for receiving the suspension of catalyst particles andhydrocarbon vapour which leave the reactor riser (10). The lower end ofthe tubular housing is fluidly connected by means of a frusto conicalwall section (13) to a dipleg (14). Through dipleg (14) most of thecatalyst particles will be discharged downwards. The upper end of thetubular housing is provided with a cover (15). Cover (15) is providedwith an axial circular opening (16) through which opening a gas outletconduit (4) protrudes.

In FIG. 1 only one secondary separator (2) is shown for clarity reasons.More than one, for example two, secondary separators (2) may be in fluidcommunication with one primary cyclone (1). Through a gas outlet conduit(17) of the secondary cyclone (2) the hydrocarbon vapours, which arepoor in catalyst particles, are discharged from the FCC reactor vesselvia plenum (24) and gas outlet (18). The vapours may be furtherprocessed in downstream product separation equipment. The secondarycyclone (2) is further provided with a dipleg (19) to dischargeseparated catalyst particles downwards.

The reactor vessel (20) further comprises at its lower end a strippingzone (21) provided with means (22) to supply a stripping medium to adense fluidized bed of separated catalyst particles, which formsstripping zone (21). Stripping medium can be any inert gas. Steam orsteam containing gasses are suitably used as stripping medium.

The reactor vessel (20) further comprises means to discharge strippedcatalyst particles from the vessel via conduit (23). Via conduit (23)stripped, or also referred to as spent catalyst, is transported to aregeneration zone (not shown). In such a regeneration zone coke isremoved from the catalyst by means of (partial) combustion. Regeneratedcatalyst is transported to the upstream part of the reactor riser whereit is contacted with a hydrocarbon feed to yield the earlier referred tosuspension of catalyst particles and hydrocarbon product vapours at thedownstream part of the reactor riser.

The reactor vessel (20) further comprises means to discharge thehydrocarbon and stripping medium vapours from the vessel via conduit(18).

The primary cyclone (1) and the secondary cyclone (2) are fluidlyconnected by means of outlet conduit (4) and inlet conduit (7). Outletconduit (4) is fluidly connected to a gas outlet opening (3) of theprimary cyclone (1). Outlet conduit (4) is at its opposite end providedwith a gas outlet opening (5).

The inlet conduit (7) is fluidly connected to the gas inlet (6) of thesecond cyclone (2). The two conduits (4, 7) are arranged co-axial suchthat gas leaving the outlet opening (5) of the outlet conduit (4) entersthe inlet opening (8) of the inlet conduit (7). Also stripping gas fromthe stripping zone (21) can enter the gas inlet opening (8) of the inletconduit (7). The gas outlet opening (5) and the gas inlet opening (8)are axially spaced away from each other.

As shown in FIG. 1 the primary cyclone (1) is fixed to the riser (10)and the secondary cyclone (2) is fixed to the upper end of vessel (20).This will result in that during start-up and cool down situations therelative distance between openings (5) and (8) may vary during to thedifferent thermal expansion of the different parts of vessel (20). Bynon-overlapping opening is here meant that there is a non-overlappingsituation at normal operating conditions.

FIG. 2 shows the upper end of the primary cyclone (1) and the lower endof the inlet conduit (7). The reference numbers have the same meaning asin FIG. 1. The interior of the gas outlet tube (4) is provided withmeans (9) to decrease the swirling motion of the gas passing said outletconduit (4). These means (9) may be baffles fixed to the inner surfaceof conduit (4). Preferably these baffles extend radialy from the surfacetowards the center of the conduit. These means (9) may be positionedalong the wall parallel to the axis (25) (as shown). Alternatively themeans (9) may be positioned under an angle relative to the axis (25)such that they are directed in the direction of the swirl but at alesser angle than the swirl itself such that a decrease in the swirlingwould still be achieved.

Opening (5) is preferably provided with a tapered opening (27) such tofurther direct the gas into opening (8). The distance (d) betweenopening (5) and opening (8) is zero or a positive value such to achievea non-overlapping opening. The distance (d) is preferably between 0 and3 times the diameter of opening (5). The diameter of opening (8) ispreferably larger than the diameter of opening (5).

The configuration of FIG. 2 further shows that the cover (15) of theprimary cyclone is provided with a frusto conical element (26), whichwill further direct the stripping gas from stripping zone (21) towardsopening (8). Such an element (26) is furthermore advantageous becausecatalyst will not deposit on the cover (15) of primary cyclone (1). Theangle (α) is preferably greater than the angle of repose of the catalystparticles, more preferably the angle α is greater than 45°. The uppervalue for this angle is between 45 and 90° and will be determined bypractical considerations such as space limitations. The invention isalso directed to a cyclone configuration wherein the cover of theprimary cyclone is provided with a titled roof (26) and wherein a slitis present in the connecting conduit between primary and secondarycyclone. The angle α is the angle which is formed by the surface ofelement (26) with the horizontal cover (15) of the cyclone.

In FIGS. 1 and 2 the openings (5) and (8) are located in the verticalpart of the conduit connecting the primary and secondary cyclone.Optionally, but less preferred, such openings may also be located in thehorizontal part of said connecting conduit.

FIG. 3 shows the top view of primary cyclone 1 illustrating thetangentially inlet connected to conduit (11) and the swirl decreasingbaffles (9) inside conduit (4) which are viewed via opening (5). Alsoshown is the upper end of conduit (4), which is slightly inward taperedend (27).

FIG. 4 shows a preferred embodiment wherein the inlet conduit (7) isprovided with a number of guiding means (28), of which only one is shownfor clarity reasons, which will, in use, further ensure that conduits(4) and (7) will remain in a co-axial position relative to axis (25).These guiding means (28) are preferably fixed to conduit (7) and willallow that conduit movement of the inlet and outlet conduits (4,7)relative to each other in the axial direction only. These guiding means(28) may also further advantageously decrease the swirling motion of thegas leaving opening (5).

Examples of FCC processes in which the apparatus according the inventioncan be suitably used are described in the afore mentioned patentpublications and those described in Catalytic Cracking of HeavyPetroleum Fractions, Daniel DeCroocq, Institut Frangais du Petrole, 1984(ISBN 2-7108-455-7), pages 100-114. Preferably the apparatus is used inan FCC process wherein a gas solids suspension if fed to the primarycyclone having a solids content of between 1 and 12 kg/m³.

1. A configuration comprising: of two cyclones for separation of solidsfrom a solids-gas mixture wherein the gas outlet of a first cyclone isfluidly connected to an outlet conduit provided with a gas outletopening and the gas inlet of the second cyclone is connected to an inletconduit provided with a gas inlet opening, wherein the outlet conduitand inlet conduit are arranged co-axial such that gas leaving the outletopening of the outlet conduit enters the inlet opening of the inletconduit and gas from the exterior of the cyclone configuration can enterthe gas inlet opening of the inlet conduit, wherein the gas outletopening and the gas inlet opening are axially spaced away from eachother and wherein the interior of the gas outlet tube is provided withmeans to decrease the swirling motion of the gas passing said outletconduit.
 2. The configuration according to claim 1, wherein the openingof outlet conduit is a tapered opening.
 3. The configuration accordingto any one of claim 2, wherein the outlet conduit and the inlet conduitare arranged along a vertical co-axial axis.
 4. The configurationaccording to claim 3, wherein the outlet conduit and the inlet conduitare kept in a co-axial position relative to each other by means ofguiding means which are attached to inlet conduit and extend to theoutlet conduit thereby allowing movement of the inlet and outletconduits relative to each other in the axial direction only.
 5. Theconfiguration according to claim 4, wherein for separation of solidsfrom a solids-gas mixture wherein the gas outlet of a first cyclone isfluidly connected to an outlet conduit provided with a gas outletopening and the gas inlet of the second cyclone is connected to an inletconduit provided with a gas inlet opening, wherein the outlet conduitand inlet conduit are arranged co-axial such that gas leaving the outletopening of the outlet conduit enters the inlet opening of the inletconduit and gas from the exterior of the cyclone configuration can enterthe gas inlet opening of the inlet conduit, wherein the primary cycloneis provided with a tilted roof.
 6. The configuration according to claim5, wherein the angle (α) formed by the tilted roof and the horizontaltop of the primary cyclone is greater than 45°.
 7. The configurationaccording to claim 6, wherein the angle (α) formed by the tilted roofand the horizontal top of the primary cyclone is greater than 45°.